Free radical dispersion polymerization of styrene in a mixture of a-propanol and tetrahydrofuran was carried out at 70 degrees C up to high conversions. The influence of the change of the critical chain length on the evolution of the insoluble polymer component was examined. Monomer conversion and the formation of the insoluble polymer component were measured in order to test a mathematical model presented in our previous article.(18) The critical polymer chain length i(o), the initiation rate constant k(d), and the ratio k(p)/k(t)(1/2) where k(p) and k(t) are propagation and termination rate constants, respectively, have been obtained and compared with those reported in the literature.